In recent years, III nitride semiconductors generally made of compounds in which N is combined with Al, Ga, In, and the like are widely used for light emitting devices, elements for electronic devices, and the like. Since the characteristics of such devices largely depend on the surface is flatness of the III nitride semiconductors at the atomic level, there is a demand for techniques for growing III nitride semiconductors having excellent surface flatness.
A III nitride semiconductor is formed by performing epitaxial growth on a substrate made of sapphire, SiC, Si, GaAs, or the like. However, the lattice constant and the coefficient of thermal expansion are significantly different between the III nitride semiconductor and such a substrate. Accordingly, when a III nitride semiconductor is grown on such a substrate, for the various reasons such as the lattice mismatch and the difference in thermal expansion coefficient, the warpage of the III nitride semiconductor formed on the substrate is increased, which makes it difficult to achieve excellent surface flatness at the atomic level. In order to address the difficulty, a GaN buffer layer on the substrate is doped with Si at a high concentration to form a heavily Si-doped GaN buffer layer and a nitride semiconductor layer is formed thereon, which is known to reduce dislocations.
For example, JP 2004-047764 A (PTL 1) discloses a nitride semiconductor having a substrate, an Si-doped GaN buffer layer having an Si concentration of 4×1019 cm−3 or more on the substrate, and a nitride semiconductor layer having a crystal structure of a single crystal formed by an epitaxial growth method on the Si-doped GaN buffer layer.